Xylanase production by submerged fermentation: screening and selection of producing fungi

Abstract

Xylanases represent a diverse group of enzymes that degrade beta-1,4-xylan into xylose, thereby breaking down hemicellulose, one of the major components of plant cell walls. There are several industries that commercially use xylanase, such as pulp and paper making industry for chlorine-free bleaching of wood pulp and waste paper recycling, in food industry as food additives to poultry, in baking industry for improving dough handling and the quality of baked products. Xylanases are often used for the extraction of coffee, plant oils and in the first stage of starch extraction. Along with pectinase and cellulase, xylanases are also often used for clarification of fruit juices. Different microbial sources of xylanolytic enzymes have been reported such as bacteria, fungi, yeast and marine algae. The aim of this research was to find new fungi strains with xylanase production potential. Production of xylanase enzyme was done by submerged fermentation (SmF) with several different fungi species (Penicillium chrysogenum, Aspergillus niger, Aspergillus oryzae, Aspergillus flavus, Mucor sp., Rhizopus sp.) by using beechwood xylan as a substrate. The strains were previously screened for xylanase activity on selective xylan agar medium (XAM) plates over a period of 10 days. Among all the tested fungi, two exhibited significant results (Penicillium chrysogenum, Aspergillus flavus) for growth on XAM and were subjected to submerged fermentation in xylan broth medium for further analysis. Enzyme activities (IU/ml) monitored for both fungi showed a trend in value increase over the course of the first days of fermentation, where enzyme from Penicillium chrysogenum reached its maximum activity od 0.291 ± 0.018 IU/ml on day 4 of the fermentation. In comparison to Penicillium chrysogenum, enzyme activity measured for Aspergillus flavus was at least two-fold greater during all 12 days of fermentation, reaching its maximum of 0.655 ± 0.046 IU/ml on day 8 of the fermentation. pH and temperature optimum were analyzed for both of the selected fungi and the obtained optimal values were pH 5 and 37°C.